Magnetic Resonance Imaging (MRI) Practice Test

How does water behave in terms of T1 and T2 relaxation times?

1. Long; long

2. Short; short

3. Long; short

4. Short; long

The correct answer is: Long; long

Water has unique properties in MRI that influence its T1 and T2 relaxation times. T1, or the longitudinal relaxation time, is the time it takes for the spins of protons in water to return to their equilibrium state after being disturbed by a magnetic pulse. T2, or transverse relaxation time, is the time it takes for the proton spins to lose coherence among themselves after the pulse. In the case of water, both T1 and T2 relaxation times are relatively long. This is due to the strong dipole-dipole interactions and the fact that water molecules are surrounded by other water molecules, which allows for efficient energy exchange and prolonged relaxation times. The long T1 time indicates that water takes a significant period to recover energy and return to its resting state, while the long T2 time indicates that the coherence of the spins remains for an extended period before they lose coherence. Understanding that water's inherent characteristics lead to long relaxation times is crucial in MRI, as it helps in interpreting images and identifying tissues. This property makes water an excellent contrast medium, as areas rich in water will produce signals that sustain longer, providing clearer and more defined images.